THE USE OF BACS FOR ECONOMIC TRAIT LOCUS IDENTIFICATION IN LIVESTOCK

432E Kleberg, Department of Animal Sciences, Texas A&M University, College Station, TX 77843 USA

Positional cloning in livestock species has become a reality in recent years due to availability of medium-density linkage maps, large insert genomic libraries and an increasing amount of human, mouse and rat genomic and EST sequence. Our lab is employing a new paradigm for positional cloning in livestock based largely on BAC libraries and comparative mapping. Using this approach, our lab is pursuing genes for a number of Economic Trait Locit (ETL) in cattle including growth, meat quality and horns. ETL are localized via interval analysis following a genome scan with 300 microsatellite markers in an Angus x Brahman F2 and backcross population. Once the initial ETL search is complete, the next step is to isolate BACs containing markers flanking the trait. These BACs are shotgun sequenced to identify genes for use in developing a comparative map with humans. The comparative map makes it possible to select candidate genes and anonymous ESTs from the human RH maps. Loci thought to be in the region are screened across the BAC library, new microsatellite markers are isolated from the BACs and integrated into the genetic map. Simultaneous to comparative mapping, a BAC contig across the region is constructed, from which additional markers are developed to narrow and refine the peak location. If no candidates remain, the region is sequenced and genes identified via homology with genomic or EST sequence from other species.